12 Mechanical and Thermal Characteristics of Irradiation Cross-linked Hydrogels
207
visualize the internal structure morphology. The cryogenically fractured film in
liquid nitrogen was mounted vertically on the SEM stub by silver adhesive paste.
The specimens were sputter coated with gold to avoid electrostatic charges and to
improve image resolution before being examined by the electron microscopy.
12.2.2.2 Mechanical Analysis
The tensile strength of the swollen polymer samples were tested using a modernized
IMASH-20-75 ALA-TOO test machine (Russia) [8]. Measurements of the static
elastic module E, elastic limit σ ¨, and yield point σ T which were carried out by
stress-strain (σ –ε) diagram at the brief monaxonic extension were plotted.
12.2.2.3 Thermogravimetric Analysis (TGA)
Thermogravimetric analysis (TGA) was done to study thermal decomposition
behavior of dried in vacuum samples using a Q50 TA Instrument (US) in nitrogen
atmosphere at a heating rate of 10 ◦ C × min −1 from 20 to 600 ◦ C. Processing of
the results was performed using specialized TA Universal Analysis program.
12.2.2.4 Differential Scanning Calorimetry (DSC)
A differential scanning calorimeter Q2000, TA Instruments (Inc., DE, USA), was
used for study of thermophysical characteristics (glass transition temperature, Tg) of
hydrogels. All the samples were previously dried up to fixed weight in vacuum. The
DSC curves were obtained by sample heating (at 5 ◦ C/min) from room temperature
to 200 ◦ C, followed by a recooling until reaching 25 ◦ C. Rescans were performed
immediately after each scan, in order to erase the thermal history of the samples
and to confirm the location of the Tg, based on the reversibility of this second-order
transition. The melting temperature (T m ) of the samples was also measured. The
results were processed using the TA Universal Analysis program.
12.3 Results and Discussion
12.3.1 Radiation Cross-linked Hydrogels
In the present study, the irradiated hydrogel dressing membranes, prepared by means
of electron beam, were obtained as 2.5–2.7-mm-thick sheets. The irradiation of
aqueous polymer solution initiates the generation of macro-radicals on polymer
chains. Radiolysis of water molecules leads to the appearance of hydroxyl radicals,
207
visualize the internal structure morphology. The cryogenically fractured film in
liquid nitrogen was mounted vertically on the SEM stub by silver adhesive paste.
The specimens were sputter coated with gold to avoid electrostatic charges and to
improve image resolution before being examined by the electron microscopy.
12.2.2.2 Mechanical Analysis
The tensile strength of the swollen polymer samples were tested using a modernized
IMASH-20-75 ALA-TOO test machine (Russia) [8]. Measurements of the static
elastic module E, elastic limit σ ¨, and yield point σ T which were carried out by
stress-strain (σ –ε) diagram at the brief monaxonic extension were plotted.
12.2.2.3 Thermogravimetric Analysis (TGA)
Thermogravimetric analysis (TGA) was done to study thermal decomposition
behavior of dried in vacuum samples using a Q50 TA Instrument (US) in nitrogen
atmosphere at a heating rate of 10 ◦ C × min −1 from 20 to 600 ◦ C. Processing of
the results was performed using specialized TA Universal Analysis program.
12.2.2.4 Differential Scanning Calorimetry (DSC)
A differential scanning calorimeter Q2000, TA Instruments (Inc., DE, USA), was
used for study of thermophysical characteristics (glass transition temperature, Tg) of
hydrogels. All the samples were previously dried up to fixed weight in vacuum. The
DSC curves were obtained by sample heating (at 5 ◦ C/min) from room temperature
to 200 ◦ C, followed by a recooling until reaching 25 ◦ C. Rescans were performed
immediately after each scan, in order to erase the thermal history of the samples
and to confirm the location of the Tg, based on the reversibility of this second-order
transition. The melting temperature (T m ) of the samples was also measured. The
results were processed using the TA Universal Analysis program.
12.3 Results and Discussion
12.3.1 Radiation Cross-linked Hydrogels
In the present study, the irradiated hydrogel dressing membranes, prepared by means
of electron beam, were obtained as 2.5–2.7-mm-thick sheets. The irradiation of
aqueous polymer solution initiates the generation of macro-radicals on polymer
chains. Radiolysis of water molecules leads to the appearance of hydroxyl radicals,